1. Technical Field
The present invention relates to bicycles, and more particularly to a shift control system used in a power-assisted bicycle.
2. Description of Related Art
As to the prior art in the field of power-assisted bicycles, Japan Patent Application Publication No. 2004-243920 has disclosed an electrically assisted bicycle, which determines whether to use an assisting power according to a pedaling force and a rotational speed of its driving wheel, so as to allow effort-saving riding experience.
Besides, a known automatic shifting system for bicycles is described in Taiwan Patent No. 583117, titled “AUTOMATIC GEAR-SHIFTING CONTROL DEVICE FOR BICYCLE AND METHOD THEREOF” or its corresponding patent, U.S. Pat. No. 6,774,771. As stated in the background paragraphs of the above-referred patents, an automatic shifting device that conducts appropriate shifting according to the running condition of the bicycle is well known in the art.
The foregoing prior-art devices only involve converting a signal sensed by a sensor into a numeral value and comparing the numeral value to gear position values of various gear positions so as to determine whether shifting is to be conducted. However, the actual riding conditions are changeable, and the shifting operation can become abrupt or bungling when influenced by a number of factors, such as steep slopes and incoherent pedaling movements. Without any solution for such a problem, the prior-art devices tend to be discomfort cyclists with rough shifting. Moreover, when the automatic shift control technology of Taiwan Patent No. 583117 combined with a power-assisted bicycle, the difference between the automatic shifting operation and the cyclists' expectation can be even more significant and discomfort the cyclists more seriously because in addition to the pedaling movements, the assisting power also brings effects to the shifting operation.